Problem: Solve for $x$ and $y$ using substitution. ${5x+5y = 5}$ ${x = 5y+7}$
Answer: Since $x$ has already been solved for, substitute $5y+7$ for $x$ in the first equation. ${5}{(5y+7)}{+ 5y = 5}$ Simplify and solve for $y$ $25y+35 + 5y = 5$ $30y+35 = 5$ $30y+35{-35} = 5{-35}$ $30y = -30$ $\dfrac{30y}{{30}} = \dfrac{-30}{{30}}$ ${y = -1}$ Now that you know ${y = -1}$ , plug it back into $\thinspace {x = 5y+7}\thinspace$ to find $x$ ${x = 5}{(-1)}{ + 7}$ $x = -5 + 7$ ${x = 2}$ You can also plug ${y = -1}$ into $\thinspace {5x+5y = 5}\thinspace$ and get the same answer for $x$ : ${5x + 5}{(-1)}{= 5}$ ${x = 2}$